The present invention relates to a method for booting a microcontroller""s application software and more particularly, to a method for reprogramming a microcontroller""s application software incorporating a versatile boot method.
In general, a microcontroller""s operation includes a process for initializing, or beginning, its own internal logic and/or intended software application, also known as a boot method. Prior art boot methods are inherently non-versatile because the boot software is fixed to a particular communications protocol and hardware platform. Due to these limitations, the boot software is not always capable of being upgraded for newer technologies and is often vulnerable to erasure during reprogramming. In many instances, the boot software cannot be reprogrammed and a reprogramming event may lead to a non-repairable fault.
Typically the boot method for a microcontroller""s application software is accomplished by the use of reset vector logic contained within the microprocessor, reset vectors in application memory space, application boot software and the application software itself. The reset vectors contain data that points to the beginning address of application boot software and other routines located in the application software. The application boot software typically determines if the application software is present and supplies the appropriate communication algorithms for reprogramming the application memory. The application software controls the functionality of the microcontroller by controlling the operations of the microprocessor. For example, before a microcontroller can be reprogrammed, the application memory space must be erased. If the reset vector is erased, or left blank, the microcontroller has no way of locating either booting or execution software for the application software upon power-on reset. The result is that the microcontroller cannot be re-booted to allow for reprogramming.
Boot-ROM technology is a one time programmable part. It cannot be reprogrammed. Boot-ROM has very limited, if any, capability for upgrading unless the part is removed and replaced with a newer version. Rapid changes in technology require the application boot software be upgraded with each version of the software in order to support changes in the communication protocol, updates to the hardware platform, or to fix known errors in the application boot software. When boot-ROM technology is used, the application boot software cannot,be upgraded; limiting flexibility and adding cost to the microcontroller.
Other known boot methods incorporate a re-programmable boot block that may introduce failure vulnerabilities during a reprogramming event. For example, during a microcontroller reset, the microprocessor will load a program counter with the starting address of the boot block. If the boot block is erased during a reprogramming event, the microcontroller has no way to boot the application software or program the memory space. In certain situations, the microcontroller may become completely inoperable. For example, if a reset occurs during a reprogramming event and the boot block has been erased, the microcontroller has no way of communicating with an external tool, which allows for the reprogramming of the boot block and/or application software.
The methods described above require high-cost drivers, are non-fail-safe, and are very non-flexible in their designs. The application boot software uses large amounts of memory space. Any upgrade requires new hardware, or introduces undesirable vulnerability to microcontroller failure. Additionally, these methods are limited to particular communications protocols and hardware technology.
In the automotive industry in particular, flexibility is key to the small controllers that are used in many automotive applications. Due to size and weight restrictions, automotive applications often employ these small controllers and the controllers are often reprogrammed for upgrades, requiring the memory be erased. Dedicating non-erasable memory space on these small controllers is contrary to the need for flexibility.
The present invention is a versatile method for reprogramming a microcontroller""s application software. The method of the present invention has a space in application memory reserved for pre-boot data. The pre-boot starting address is always fixed and its reset vector pointer cannot be erased. Therefore, the pre-boot starting address is directly referenced in the reset vector space. The purpose of the pre-boot space is to locate valid application boot software in the micro-controller""s memory space. The pre-boot space allows the application boot software to be relocated throughout the memory space during a reprogramming event without making the microcontroller vulnerable to failure. The multiple locations for the application boot software allow for a fail-safe method for reprogramming.
According to the method of the present invention, the versatile boot method divides memory into four separate memory spaces; reset vector memory space, pre-boot logic space, a main block in the application software memory space and a back-up block in the application software memory space. In the method of the present invention, a block of the application software memory space is erased and programmed with a back-up application boot. The main block of the application memory is then erased and re-programmed. Finally, the back-up block is erased and reprogrammed with application software. The microcontroller now has upgraded application boot software, reprogrammed communications software and reprogrammed application software without introducing vulnerabilities.
It is an object of the present invention to create a fail-safe method for reprogramming application software in a microprocessor. It is another object of the present invention to allow a complete update of application software including communication software. Yet another object of the present invention is to provide a method for allowing a microprocessor reset to occur during the reprogramming process of application boot memory space.
Other objects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiments and when taken in conjunction with the attached drawings and appended claims.